inteligent routing in nginx

nginx.conf

#user  nobody;
worker_processes  1;

#pid        logs/nginx.pid;

events {
    worker_connections  1024;
}


http {
    include       mime.types;
    default_type  application/octet-stream;

    sendfile        on;

    keepalive_timeout  65;

    upstream redis {
       server localhost:6379;
       keepalive 1024;
    }

    upstream app1 {
        server localhost:5001;
    }

    upstream app2 {
        server localhost:5002;
    }


    server {
        listen       80;
        server_name  localhost;

        #charset koi8-r;

        #access_log  logs/host.access.log  main;


	location /redis_check_for_v3 {
	    internal;
	    
	    #is this domain in the Redis set v3:domain?
	    redis2_query sismember v3:domain $host;

	    redis2_connect_timeout 200ms;
	    redis2_send_timeout 200ms;
	    redis2_read_timeout 200ms;
	    redis2_pass redis;
	    
	    error_page 500 501 502 503 504 505 @redis_error;
	}

	location @redis_error {
	    internal;
	    content_by_lua 'ngx.print("ignore_this_error");';
	}

        location / {
	    set $root "/var/www/app1/public";
	    set $backend "http://app1";

	    # Any proxy configuration we need, and other Nginx config if required. 
  	    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
  	    proxy_set_header Host $http_host;
  	    proxy_set_header X-Real-IP $remote_addr;

	    rewrite_by_lua '
                local host = ngx.var["host"];
                local result = ngx.location.capture("/redis_check_for_v3", { args = { host = host}});
                
		if result.body == ":1\\r\\n" then
		    ngx.log(ngx.NOTICE, "Detected v3:domain for host: ", host, ", will now route to app2");
		    ngx.var.backend = "http://app2";
                    ngx.var.root = "/var/www/app2/public";
                end
             ';

            root   $root;
	    if (!-f $request_filename) {
	 	proxy_pass $backend;
	    }
        }
}